1. Field
The present invention relates generally to wireless communications and more specifically to multi-antenna receive diversity in a wireless communication system.
2. Background
Mobile multi-antenna receive diversity refers to the use of multiple receivers in a wireless communications device. A different antenna provides input to each individual receiver, thereby providing diversity to the communications link. The diversity improves call and data transmission quality and also increases the network capacity. The multiple antennas provide spatial diversity as each multipath appears differently at each antenna. Therefore, the effects of multipath fading are not strongly correlated among the receivers. The outputs of the multiple receiver chains are combined in order to provide a better estimation of the symbols prior to decoding. Combination methods known in the art include, but are not limited to, Minimum Mean Squared Error (MMSE) combining, maximal-ratio combining, equal-gain combining, and selection combining. The main drawback of mobile receive diversity is that each receiver chain expends power, particularly in the Radio Frequency (RF) and analog portions of the chain.
Studies have shown multi-antenna receive diversity increases the forward link capacity significantly. The capacity increase may be capitalized as higher throughput, lower base station transmit power, lower Frame Error Rate (FER), or a combination of thereof. One drawback of multi-antenna receive diversity is the power cost of implementing and operating such receivers. In addition, the benefits of multi-antenna receive diversity may not always be utilized or even needed.
There is a need, therefore, to control when receive diversity is used and when it is not used. There is a need in the art for control methods and apparatuses to use mobile diversity when the benefits of greater link capacity, higher throughput, lower transmit power, lower error rate, etc. are required, and not to use mobile diversity when the benefits do not justify the higher power cost. Furthermore, there is a need to control the diversity to optimize the tradeoff between multiple multi-antenna receive diversity and power consumption in a wireless communications device.